1. Field of the Invention
The present invention generally relates to a particulate accumulation amount estimating system; More particularly, the present invention relates to a technology for estimating the amount of particulate matter accumulated in particulate filters, which are mainly used for after-processing the exhaust gas of diesel engines.
2. Background Information
Conventionally, the particulate matter (also called “particulates”) contained in the exhaust gas discharged from a diesel engine is captured using a particulate trapping device such as a diesel particulate filter. Basically, a diesel particulate filter has a honeycomb monolith made of ceramic or the like that is generally used for removing particulate matters emitted from a diesel engine. During operation of the engine, the particulate is accumulated on the diesel particulate filter increasingly. At some time when the accumulated amount of particulate exceeds an allowable amount, the diesel particulate filter becomes clogged and the exhaust pressure rises. This situation adversely affects the operating performance of the engine. For this reason, the accumulated particulate is burnt periodically so as to prevent clogging of the particulate filter.
Although the particulate matter accumulated in the particulate filter is periodically burned to prevent the filter from becoming clogged, there are components (hereinafter called “ash”) of the particulate matter that cannot be burned when the particulate filter is regenerated and thus remain in the particulate filter.
Japanese Laid-Open Patent Publication No. 2004-211650 (corresponding to U.S. Pat. No. 6,928,809) discloses a system that estimates the amount of accumulated ash based on the distance the vehicle has traveled, estimates the amount of accumulated particulate matter based on the pressure difference across the particulate filter, and subtracts the estimated ash accumulation amount from the estimated particulate accumulation amount to obtain a final particulate accumulation amount. This publication also discloses that the accumulated ash amount can be determined based on both the pressure difference and exhaust flow rate at the timing of regeneration completion. However, this publication is silent on how the accumulated ash is held within the filter passage.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved particulate accumulation amount estimating system. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.